The exceptional mechanical and physical properties observed for carbon nanotubes has stimulated the development of nanotube-based composite materials. Such properties observed at the nanoscale have motivated researchers to utilize carbon nanotubes as reinforcement in composite materials. At the nanoscale, the structure of the carbon nanotube strongly influences the overall properties of the resulting nanotube-based composite material. Carbon nanotubes are believed to have elastic moduli on the order of 1 TPa (1000 GPa) with strengths in the range of 30 GPa, in addition to exceptionally high electrical and thermal conductivity. These properties, combined with recent advances, have generated considerable interest in utilizing carbon nanotubes as nanoscale reinforcement in composites. Research has shown that the change in length scale of carbon nanotubes relative to carbon fibers enables selective reinforcement of the polymer matrix surrounding a carbon fiber. Local stiffening due to nanotubes results in improved load transfer at the fiber/matrix interface.
Although exceptional electrical, thermal, and mechanical properties of carbon nanotubes have been researched, expected property enhancements in composites have not been realized. One of the most significant challenges in improving the properties of nanocomposites based on carbon nanotubes is to obtain a uniform dispersion of nanotubes within the polymer matrix, which is needed to achieve good reinforcement in a composite. Because of their small size, carbon nanotubes tend to agglomerate when dispersed in a polymeric resin. In addition to slipping of nanotubes that are not adhered to the matrix, aggregates of nanotube bundles effectively reduce the aspect ratio (length/diameter) of the reinforcement.